JP2008198850A - Solenoid current control apparatus and method - Google Patents

Abstract

A solenoid current control device and a current control method capable of stably controlling a solenoid current even when the ambient temperature of the control device changes are provided.
In order to eliminate an error due to a change in offset voltage due to a change in ambient temperature of the control device, an error is eliminated by calculating an offset voltage while the control device is operating and performing control according to the value. The offset voltage value when the solenoid current is 0 A may be used as the offset voltage value. In order to set the solenoid current to 0 A, the switching transistor connected in series with the solenoid may be turned off.
[Selection] Figure 6

Description

  The present invention relates to a current control apparatus and method for feeding back a solenoid current to a target current.

  Conventionally, as a method for improving current control accuracy in a solenoid current control device, there is one disclosed in Patent Document 1. This is because the variation of the circuit elements of the current detection circuit is corrected for each control device at the manufacturing stage of the device, the correction value is stored for each device, and the error is reduced by using the current control by the correction value. is there.

JP 11-327602 A

  The correction value according to Patent Document 1 takes into account the variation of circuit elements found in the manufacturing stage, but is sufficient for the temperature change of the circuit characteristics inside the control device due to the ambient temperature change of the control device in the operation stage. Not considered. Therefore, there is a case where the circuit characteristics cannot be properly corrected by using a correction value set in the manufacturing stage due to a temperature change during operation. When the ambient temperature of the control device changes from the temperature at which the correction value is stored and the offset voltage of the current detection circuit changes due to the temperature characteristics of the circuit elements constituting the current detection circuit, an error occurs in the current detection value. Will occur.

  The present invention has been made in view of such a situation, and provides a solenoid current control device and a current control method capable of stably controlling the solenoid current even when the ambient temperature of the control device changes. is there.

  In order to solve the above problems, in the present invention, in order to eliminate an error due to a change in offset voltage due to a change in ambient temperature of the control device, an offset voltage is calculated while the control device is operating, and control is performed based on the value. By doing so, errors are eliminated. The offset voltage value when the solenoid current is 0 A may be used as the offset voltage value. In order to set the solenoid current to 0 A, the switching transistor connected in series with the solenoid may be turned off.

  That is, the solenoid current control device according to the present invention has a current detection circuit for detecting a current flowing through the solenoid, and duty-controls a switching element connected in series to the solenoid based on the detected current value. A solenoid current control device, comprising: a control unit that detects an output of a current detection circuit when the switching element is in an OFF state, that is, a duty of 0%, as a current zero point, and performs current control using the detected output. It is characterized by providing. The detected current zero point output is used for current control until the switching element is turned off next time.

  Further features of the present invention will become apparent from the best mode for carrying out the present invention and the accompanying drawings.

  According to the present invention, it is possible to stably control the current of the solenoid even if there is a change in the ambient temperature of the control device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it should be noted that this embodiment is merely an example for realizing the present invention and does not limit the present invention. In each drawing, the same reference numerals are assigned to common components.

<Configuration of electronic control device>
FIG. 1 is a block diagram showing a schematic circuit configuration of an electronic control unit 1 (hereinafter, ECU) for an automatic transmission according to an embodiment of the present invention.
The ECU 1 controls the transmission of the automobile, and includes a clutch solenoid 2 that controls the clutch, a line pressure solenoid 4 that controls the hydraulic pressure of the transmission, a shift solenoid A 5 that selects a transmission gear ratio, and a shift solenoid. The operation of B 6 is controlled according to a program set in advance in the microcomputer 21 in accordance with the engine state sent from the engine ECU 11 and the signal supplied from each sensor.

  The microcomputer 21 takes in signals from the clutch rotation sensor and the engine rotation sensor 9 via the rotation sensor input circuit 24, and controls the current of the clutch solenoid 2 to a target current with reference to, for example, a table, thereby determining the coupling state. Control. That is, the clutch coupling force is increased by increasing the solenoid current. Note that the solenoid current of the released clutch is 0A.

<Configuration of Clutch Solenoid Drive Circuit 27>
FIG. 2 is a diagram showing a detailed configuration of the drive circuit 27 of the clutch solenoid 2. In FIG. 2, the drive circuit 27 is connected in series to the clutch solenoid 2, and includes a transistor 41 that is duty-controlled by PWM by the microcomputer 21, a current detection resistor 43 for detecting the current of the clutch solenoid 2, and a transistor 41. A free-wheeling diode 42 for flowing the return current of the solenoid when OFF is provided, and a current detection circuit 44 for detecting the current flowing through the current detection resistor 43.

  The current of the clutch solenoid 2 is amplified by the current detection circuit 44 (amplifier circuit) at the both ends of the current detection resistor 43 and input to the A / D converter of the microcomputer 21. The microcomputer 21 calculates a drive duty (PWM control) from the difference between the solenoid current value input to the A / D converter and the target current value, and outputs it to the transistor 41.

  FIG. 3 is a diagram for explaining PWM control for setting the current flowing through the clutch solenoid 2 to the target current. 3A shows the ON / OFF period of the transistor 41, and FIG. 3B shows the change in the current of the clutch solenoid 2 due to the ON / OFF of the transistor 41. FIG. FIG. 3C is a diagram showing a change in current of the clutch solenoid 2 due to a change in drive duty. When the transistor 41 is ON, the current flows from the battery 12 → the transistor 41 → the clutch solenoid 2 → the resistor 43 → the ground, and the current flowing through the current detection resistor 43 increases with time (see FIG. 3B). When the transistor 41 is OFF, the current stored in the clutch solenoid 2 flows through the clutch solenoid 2 → the current detection resistor 43 → the free wheel diode 42 → the clutch solenoid 2, and the current flowing through the current detection resistor 43 decreases with time. . Therefore, the target current (average current) can be controlled by controlling the ON / OFF period of the transistor 41.

<Configuration of Current Detection Circuit 44>
FIG. 4 is a diagram showing a detailed circuit configuration of the current detection circuit 44. In FIG. 4, the current detection circuit 44 includes a differential amplifier circuit 51 using an operational amplifier and an offset voltage circuit 52. One side of the current detection resistor 43 is connected from the P-GND terminal 60 through the harness 61 to the body GND 63 of the vehicle. The offset voltage 58 is supplied to the differential amplifier circuit 51 so that the differential amplifier circuit 51 operates normally even if P-GND swings to the negative side with respect to the GND potential of the differential amplifier circuit 51.

  FIG. 5 shows the output characteristics of the current detection circuit (amplification circuit) 44. As shown in FIG. 5, the differential amplifier circuit output voltage at the solenoid current 0A is the offset voltage. Here, when the slope of the output voltage V with respect to the solenoid current I is k and the offset voltage is Vo, the output voltage V of the differential amplifier circuit 51 is the output voltage V = k · I + Vo. Therefore, the current I can be obtained from the output voltage V by I = (V−Vo) / k.

  Here, the offset voltage 58 is obtained by dividing the reference voltage Vref 56 by the resistors R1 53 and R2 54 in the offset voltage circuit 52 of FIG. 4, and the obtained offset voltage 58 passes through the operational amplifier 55 (buffer). Are input to the differential amplifier circuit 51.

  The resistance value of the reference voltage Vref56 and R1 53, R2 54 changes due to a change in the ambient temperature of the ECU 1, and the offset voltage also changes due to its action. If this offset voltage changes, an error occurs in the detected value of the solenoid current, and the solenoid current cannot be stably controlled. This situation will be described with reference to FIG. When the ambient temperature of the ECU 1 changes from Ta0 to Ta1, it is assumed that the offset voltage changes from Vo (Ta0) to Vo (Ta1). Then, the output voltage 57 of the differential amplifier circuit 51 also shifts by Vo (Ta1) −Vo (Ta1), and this amount becomes an error in the control current.

  Therefore, in order to reduce this error, it is understood that when the ambient temperature of the ECU 1 reaches Ta1, control is performed using Vo (Ta1) as an offset voltage.

  Vo (Ta1) can be detected by measuring the output voltage 57 of the differential amplifier circuit 51 when the transistor 41 is turned off and the solenoid current is zero, which becomes the offset voltage Vo (Ta1). Then, this value may be stored in the microcomputer 21 and used as the current control offset voltage until the solenoid current becomes zero next time. Control is performed such that the PWM pulse width is reduced when the offset voltage Vo is large, and the PWM pulse width is increased when Vo is small.

<Specific operation of current detection of clutch solenoid>
FIG. 6 is a flowchart for explaining the current detection method of the clutch solenoid 2. First, an operation for learning the offset voltage value of the clutch current detection circuit is executed (see FIG. 6A).
In gear shifting, the clutch that is engaged is once released, the gear ratio of the transmission is changed by a shift operation, and the clutch is engaged again. When opened, the transistor 41 connected in series with the clutch solenoid 2 is turned off (S1), and the clutch solenoid current is set to zero (S2). Then, the output voltage 57 of the differential amplifier circuit 51 at that time is detected and stored in the RAM as an offset voltage value (S3).

  Next, when the clutch is engaged (see FIG. 6B), the current detection method A / D converts the clutch solenoid current detection circuit output voltage V1 (S4). Then, using the Vo stored in S3, the solenoid current I = (V1−Vo) · k is calculated (S5).

  By this method, the value of the offset voltage of the current detection circuit can be used for control during operation of the control device, and errors due to changes in ambient temperature can be reduced.

<Summary>
As described above, the present embodiment has a current detection circuit that detects a current flowing through the solenoid, and performs duty control on the switching element connected in series to the solenoid based on the detected current value. The present invention relates to a current control device. The output (offset voltage) of the current detection circuit when the switching element is in the OFF state is detected as the current zero point, and current control is performed using the detected offset voltage. Thereby, since the offset voltage value obtained when the control device is operating can be used for the control, the error of the offset voltage value that varies depending on the temperature of the control device can be reduced, and the current control accuracy is improved.

The detected offset voltage is used for current control until the switching element is turned off next time. Thus, since the offset voltage value used for current control is sequentially updated, the error of the offset voltage value that changes due to the temperature of the control device can be reduced.
Such a control method is preferably applied to a solenoid that is turned off during operation, and is preferably used, for example, for current control of a clutch solenoid.

It is a block diagram of an electronic control unit (ECU) of an automatic transmission. 3 is a block diagram of a solenoid drive circuit 27. FIG. It is a figure for demonstrating the PWM control for setting the electric current which flows into the clutch solenoid 2 to a target electric current. 3 is a circuit diagram of a current detection circuit 44 of a solenoid drive circuit 27. FIG. It is a solenoid current-output voltage characteristic of a current detection circuit. It is a flowchart for demonstrating an electric current detection process.

Explanation of symbols

1 Electronic transmission electronic control unit (ECU)
2 Clutch solenoid 12 Battery 21 Microcomputer 27 Clutch solenoid drive circuit 41 Transistor 42 Free wheel diode 43 Current detection resistor 44 Amplification circuit 51 Differential amplification circuit 52 Offset voltage circuit 53, 54 Resistor 55 Operational amplifier 56 Reference voltage

Claims (6)

A current control device for a solenoid having a current detection circuit for detecting a current flowing through the solenoid and duty-controlling a switching element connected in series to the solenoid based on a current value of the detected current,
A solenoid current control apparatus comprising: a control unit that detects an output of the current detection circuit when the switching element is in an OFF state as a current zero point, and performs current control using the detected output.   2. The solenoid current control apparatus according to claim 1, wherein the control unit uses the detected output of the current zero point for current control until the switching element is turned off next time.   The solenoid current control device according to claim 1, wherein the solenoid is a clutch solenoid. A solenoid current control method for detecting a current flowing through a solenoid by a current detection circuit and duty-controlling a switching element connected in series to the solenoid based on a current value of the detected current,
A solenoid current control method comprising: detecting an output of the current detection circuit when the switching element is in an OFF state as a current zero point; and performing current control using the detected output.   The solenoid current control method according to claim 4, wherein the detected current zero point output is used for current control until the switching element is turned off.   6. The solenoid current control method according to claim 4, wherein the solenoid is a clutch solenoid.

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